At present, there is a technology called “imaging” or “imaging technology”. In the imaging technology, some fluorescent material is injected into a biological body followed by the aggregation of the fluorescent material near a particular area of the body, and then the aggregated fluorescent material is observed from outside the body. For this reason, the fluorescent material is expected as a useful material in the imaging technology. In this technology, not only safety and stability are required for the fluorescent material, but also a high penetrating power of excitation light and fluorescence to biological materials is required. From this point of view, an organic fluorescent material that emits light having from ultraviolet wavelengths to visible wavelengths as well as a quantum dot-substance, for example, has problems with a fluorescent stability, a toxicity and a penetrability of fluorescence.
The present invention is directed to solve the above problems. That is to say, an object of the present invention is to provide a favorable fluorescent particle in terms of a penetration of fluorescence and excitation light into biological materials so that the particle can be suitably used in the imaging technology and the like.